1. Technical Field of the Invention
This invention relates to substrate processing apparatus for cleaning a substrates, for example, semiconductor wafer, glass for LCD glass, etc.
2. Description of the Related Art
For instance, in the manufacturing process of semiconductor devices, it is carried out to clean semiconductor wafers (called as “wafers” hereinafter) by a processing liquid, such as chemical liquid or pure water, in order to remove various contamination, for example, particles, organic pollutant, metallic impurities, etc. from the wafers. For example, when applying a dry-chemical processing on a resist film painted on the wafer, there is formed, on the surface of the resist film, a new resist film which is different from the former resist film in quality and which will be remained as an foreign substance. The foreign substances of the resist film having a changed quality are eliminated by cleaning the wafers after the dry chemical processing. As to the substrate cleaning apparatus performing the above cleaning process, there are known substrate cleaning apparatuses of various kinds, for example, batch-type, single-wafer type, spin-type, etc. In a cleaning system equipped with the substrate cleaning apparatus, there is arranged a circulatory unit for collecting and recycling the processing liquid used in the substrate cleaning apparatus in view of saving the consumption of the processing liquid used for the cleaning operation. For example, the processing liquid discharged from the substrate cleaning apparatus is fed to the circulatory unit through a recovery path and continuously collected into a storage part, for example, a tank in the circulatory unit. The so-collected processing liquid is sucked up by a pump and fed to the substrate cleaning apparatus again. During this recovery process, it is performed to make the so-sucked processing liquid pass through a filter in order to recover the cleanness of the processing liquid for reuse.
However, the conventional substrate cleaning apparatus has a problem that if the cleaning process follows one process which is apt to produce relatively large foreign substances (e.g. dry/chemical process for resist film), the recovery path and pipes in a circulatory system are easy to be blocked with the foreign substances. Therefore, it has been required to clean the pipes etc. frequently. Furthermore, the filter for cleaning the processing liquid has been apt to be blocked with the foreign substances. Therefore, it has been required to exchange the filter frequently, causing the maintenance fee of the apparatus to be raised. Additionally, since the exchange work of the filter and the pipes in the circulatory system requires interrupting the cleaning process of the wafer, the requirement has caused a deterioration of the whole throughput of the apparatus in processing the wafers.